Keywords

Coronary artery occlusion. Collateral circulation. Conus artery.

Abstract

The prognosis of patients with coronary artery disease largely depends on the presence of a collateral circulation. The location and extent of the collateral circulation is highly variable and these parameters determine whether or not ischemic symptoms occur and whether left ventricular contractility is abnormal. The collateral circulation is generally established through small-caliber distal vessels, although many different forms have been described. We report on three patients with severe left coronary artery disease and collateral circulation through a large conus coronary artery that joined a proximal or medial segment of the left anterior descending coronary artery. In all three cases, left ventricular function was preserved.

Article

INTRODUCTION

The first artery that originates in the right coronary
artery (RCA) is the pulmonary conus artery, or conus
artery. In a variable proportion of the population
(between 30% and 50%), this artery originates in an
independent ostium in the right sinus of Valsalva,
anterior and superior to the ostium of the RCA.1

When this is the case, this artery is described as "the
third coronary."2 The anterior and superior course of the conus artery is usually short, and irrigates the
pulmonary infundibulum and the supraventricular
crest. Occasionally, it forms an anastomosis with
the left anterior descending artery (left conus
artery), thus forming the so-called "arterial circle
of Vieussens." In the present article, we describe
the clinical and angiographic characteristics of 3
patients with occlusion in the left coronary artery
and collateral circulation through a large conus
artery up to the proximal and medial segment of the
anterior descending artery.

METHODS

The patients described in this article were
admitted to our center between February 2006 and
December 2008. They all underwent cardiological
studies due to angina-like precordial pain
episodes. Diagnosis was conducted using coronary
angiography and 64-slice multidetector computed
tomography (MDCT).

RESULTS

The clinical and angiographic characteristics of
the patients are described below and presented in
Table.

Case 1

A 54-year-old man, smoker, with
hypercholesterolemia, was referred to the center
due to stable effort angina pectoris of 3 years
duration. He presented inferior Q wave in the basal
electrocardiogram (ECG). The echocardiogram
showed inferoposterior hypokinesia with a left
ventricular ejection fraction (LVEF) of 55%.
Coronary angiography demonstrated an independent
origin of the LAD and circumflex arteries. The LAD
was proximally occluded, and it was impossible to
view its distal bed. The RCA was occluded at the
distal segment and received homocoronary and
heterocoronary collateral vessels from the circumflex
artery. Given that anterior contractility was normal,
and that coronary revascularization was planned,
MRCT was requested to assess the bed distal to
the LAD occlusion. The MRCT revealed a conus
artery with an independent origin in the right sinus
of Valsalva and that provided flow to the LAD from
its medial segment and filled its distal bed (Figure 1).
Based on these findings, myocardial revascularization
was indicated, but the patient refused this procedure.
The symptoms improved, but did not disappear, after
intensifying the medical treatment.

Figure 1. Case 1. A: anteroposterior view
of left coronary angiography; the anterior
descending artery is occluded at a
proximal level. B: MRCT image processed
with MPR (multiplanar reformatting)
that shows an occluded segment in the
anterior descending artery. C and D: 3D
volume rendering reconstruction of MRCT
that shows the course of the conus artery
until it joins the anterior descending
artery.

Case 2

A 74-year-old man, smoker, was admitted to
our center due to unstable angina. The basal ECG presented left anterior hemiblock. During
admission, he presented a new episode of precordial
pain and ECG showed ST-segment elevation
of 1 mm in aVR and aVL, with a ST-segment
depression of 2 mm in V4-V6 and in leads II and III
and aVF. Transthoracic echocardiogram showed
mild anterolateral hypokinesia, with an LVEF of
50%. Coronary angiography demonstrated total
occlusion of the left main coronary artery (LMCA)
at its proximal segment. The LAD was filled by the
collateral circulation through a large conus artery
that originated within the right sinus of Valsalva,
very close to the ostium of the RCA. It coursed with
the LAD at the medial segment after following a
long and tortuous course. The circumflex artery was
not visualized and the RCA was dominant without
any significant stenosis. In order to evaluate the
relationship between the conus collateral circulation
and the sternum before the intervention, MRCT
was conducted and this showed a coronary anatomy
that matched with the results of the coronary
angiography (Figure 2). Coronary revascularization
was conducted using a left internal mammary artery
graft to the medial segment of the LAD. Patient
evolution was good.

Figure 2. Case 2. A: anteroposterior
view of left coronary angiography; the
left main coronary artery is occluded at
the proximal level. B: left anterior oblique
view of coronary angiography showing
the long and tortuous course of the
conus artery. C: multidetector computed
tomography image processed with MPR
(multiplanar reformatting) that shows
occlusion in the left main coronary artery,
and that includes the proximal part of
the anterior descending and circumflex
arteries. D: 3D reconstruction of MRTC
that shows the course of the conus
artery.

Case 3

A 60-year-old hypertensive man, surgically
treated 12 years earlier for aneurysm in the aortic
root. A composite Dacron tube graft with a
Carpentier bioprosthetic valve was implanted
and coronary reimplantation performed using the
Cabrol technique. He was admitted to hospital with
symptoms of progressive effort angina pectoris.
The ECG showed negative and nonspecific T waves
in V1-V2. Global and regional wall motion were normal on echocardiogram. Catheterization of the
left coronary artery during coronary angiography
was not successful. However, this artery was filled
from the RCA through a large conus artery that
connected with the LAD at its proximal segment.
Due to the patient's history of aortic surgery, the
failure to catheterize the left coronary artery, and
the need to plan the best surgical approach, MRCT
was conducted. It demonstrated proximal occlusion
of the LMCA and collateral circulation through the
conus artery, with excellent angiographic correlation
(Figure 3). The patient underwent coronary
revascularization and the left mammary artery used
as a sequential graft to the ramus intermedius and
the LAD. Patient evolution was good.

Figure 3.
Case 3. A: aortogram where
the left coronary trunk is not visualized;
the left coronary artery is filled through
the conus artery. B: 3D reconstruction of
MRTC that shows the course of the conus
artery.

DISCUSSION

Collateral circulation is a key factor fact in the
pathophysiology of coronary disease. The symptoms
and prognosis among coronary patients depend on
the quality of collateral circulation. We describe 3
patients of left coronary tree occlusion and collateral
circulation via a large conus artery which joined the
LAD after following a long and tortuous path. This anatomy could be considered a particular form of
the so-called "circle of Vieussens," but the conus
artery did not present secondary ramification or a
capillary network in any of the patients. In patients
1 and 2, the conus artery presented an independent
outlet in the right sinus of Valsalva. The first patient
also had the peculiarity of presenting 4 different
coronary ostia, since the LAD and the circumflex
also presented independent ostia.

The collateral circulation from the conus artery
was probably crucial, as deduced by the presence
of preserved or minimally affected general and
regional ventricular functions, regardless of other
physiological factors (eg, ischemic preconditioning).
Our report emphasizes the importance of always
looking for anatomical variants on coronary
angiography, especially when LMCA occlusion or
equivalent is present and preserved left ventricular
function.3 In up to 20% of coronary angiographies,
the conus artery is not visualized, mainly due to its
independent origin or within the first millimeters
of the RCA.1 The clinical implications of this
are not only diagnostic, but also therapeutic. It is
fundamental for the surgeon to know the origin
of the conus artery and its course in order to avoid causing damage during surgery. Surgical
interventions involving manipulation of the right
infundibulum present the risk of damaging the
conus artery, especially when it is partially hidden
by an intramyocardial pathway. In the percutaneous
treatment of chronic occlusion of the LAD,
simultaneous injection through the conus artery
has been described as useful in visualizing the distal
segment of LAD and advancing the guide correctly. It could even serve as an alternative to the retrograde
route when the lesion cannot be successfully crossed
using an anterograde approach.3

Multidetector computed tomography has recently
been developed for the study of coronary disease.
One of the applications of this new technique is
the study of distal beds in patients with coronary
occlusion.4 This is of special interest in patients
referred to surgical coronary revascularization.

Case 1 is a good example of this application,
since the distal LAD could not be visualized during
coronary angiography. Multidetector computed
tomography is the definitive test to study variants
in coronary anatomy that could be overlooked in
coronary angiography.

In patients 2 and 3, there was chronic occlusion of
the LMCA, a very infrequent angiographic finding
(between 0.03% and 0.06%, according to different
series).5 The clinical signs are nonspecific and cannot
be distinguished from other less severe forms of
coronary disease. The presence of ventricular wall
motion abnormalities is quite common, whereas
normal ventricular function is an exception.6

In conclusion, we emphasize the usefulness of
MRCT for the study of distal beds in patients
with coronary occlusion, as well as for studying
the collateral circulation, especially when there
is a conflict between the findings of coronary
angiography and ventricular function.